Novel selective etching method for silicon nitride films on silicon substrates by means of subcritical water

The reaction of silicon nitride films on silicon substrates in sub- and sup ercritical water at temperatures between 100 and 400 degreesC has been stud ied for the first time. The etching rates for the silicon nitride films wer e higher than those for silicon dioxide films under the same conditions. A novel selective etching method for silicon nitride films using subcritical. water has been proposed, The etching mechanism for silicon nitride films i n subcritical water was studied by means of infrared spectroscopy and ion c hromatography. The etching selectivity at 200 degreesC and 10 MPa reached 7 0. An etching rate of 7.5 nm/min for the silicon nitride films was obtained under the same conditions. The selectivity value was higher than that of t he conventional method using phosphoric acid, while the etching rate was co mparable. Moreover, water is nontoxic; therefore, the proposed method is en vironmentally friendly. The proposed selective etching method for silicon n itride films using subcritical water is one of the promising candidates for future etching technologies.